LA‐ICP‐MS Zircon U‐Pb Dating of Intermediate‐Acidic Intrusive Rocks and Molybdenite Re‐Os Dating from the Bangpu Mo (Cu) Deposit, Tibet and its Geological Implication

AbstractThe multi‐stage intrusions of intermediate‐acid magma occur in the Bangpu mining district, the petrogenic ages of which have been identified. The times and sequences of their emplacement have been collated and stipulated in detail in this paper by using the laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) zircon U‐Pb dating method. The ages of biotite monzogranite that were formed before mineralization in the southwest of this mining district are 70±1 Ma (mean square of weighted deviates (MSWD) = 9.5, n= 8) and 60.60±0.31 Ma (MSWD=3.8, n= 16), which belong to the late Cretaceous–early Paleocene in age. That means, they are products of an early tectonic‐magmatic event of the collision between the Indian and Asian continentals. The ages of ore‐bearing monzogranite porphyry and ore‐bearing diorite porphyrite are 16.23±0.19 Ma (MSWD= 2.0, n= 26) and 15.16±0.09 Ma (MSWD=3.9, n= 5) separately, which belong to the middle Miocene in age; namely, they are products of the Gangdese post‐collision extensional stage when crust‐mantle materials melted and mixed as well as magmatic intrusion simultaneously occurred. Some zircons with ages of 203.6±2.2 Ma (MSWD=1.18, n= 7) were captured in the ore‐bearing diorite porphyrite, which shows that there had been tectono‐magmatic events in the late Triassic–early Jurassic. Molybdenum (copper) ore‐bodies produced in the monzogranite porphyry and copper (molybdenum) ore‐bodies produced in the diorite porphyrite are the main ore types in this ore deposit. The model ages of Re‐Os isotopic dating for the 11 molybdenite are 13.97–15.84 Ma, while isochron ages are 14.09±0.49 Ma (MSWD=26). The isochron ages of seven molybdenite from molybdenum (copper) ore with monzogranite porphyry type are 14.11±0.31 Ma (MSWD=5.2). There is great error in the isochron ages of four molybdenite from copper (molybdenum) ore with diorite porphyrite type, and their weighted average model ages of 14.6±1.2 Ma (MSWD=41), which generally represent the mineralization age. The results about the Re‐Os isotopic dating of molybdenite in the ore of different types have limited exactly that, the minerlazation age of this ore deposits is about 14.09 Ma, which belongs to the middle Miocene mineralization. The Bangpu deposit has a uniform metallogenic dynamics background with the porphyry type and skarn‐type deposits such as Jiama, Qulong and others.